George Raymond Gage 23 



(lot 5), in which case the seed received larger amounts of inoculum 

 than did the blossom-inoculated seed, an infection of only 29 per cent 

 resulted. The spores on the outside of the glumes (lot 4) produced only 

 3.1 per cent of smutted plants. 



In lot 7 of the glumeless variety, 61 per cent of smutted plants were 

 obtained from seed in which the mycelium in or on the pericarp, and 

 possibly som n adhering spores, were blamable. Since examination of 

 this seed also showed that few spores do remain ungerminated after inoc- 

 ulation, the 61 per cent is certainly largely due to mycelium and not to 

 spores. By way of contrast, spores dusted on the seed after harvest (lot 

 8) in amounts exceeding those applied at flowering time, resulted in 

 (inly 24 per cent of smutted plants. 



The procedure for ('. levis, therefore, is practically the same as for V . 

 an inn. The majority of the smutted plants are due to the invasion of 

 the plants by mycelium al ready present in the pericarp of the seed from 

 which they develop, and not from overwintered spores or pathogene 

 structures in or on the glumes. It should be noted that in every case 

 the resulting smut percentage for U. levis was somewhat larger than that 

 for U. a venae. 



Granting that some seedling invasion may result from spores which 

 remain dormant, and also from mycelium in the glumes, it is still very 

 evident that the majority of such invasions in both oat smuts are the 

 result of mycelium developed in or on the pericarp from spores which 

 lodge inside of the blossoms at pollination time. Careful examination of 

 such seed revealed mycelium only in. on, or under the epidermis of the 

 pericarp, and never in the embryo tissues. This absence of mycelium 

 in the embryo is confirmed by the success obtained in controlling the dis- 

 ease by formaldehyde. If mycelium existed in the internal parts of the 

 seed, the penetration of formaldehyde necessary to eliminate the patho- 

 gene would probably kill the seed also. 



Since the formaldehyde treatment has been successful in the control 

 (if the loose smut of barley (Tisdale and Tapke, 1924:264), it may be 

 that the mycelium in the hat-ley seed is also located largely in the peri- 

 carp. This lias been suggested by these writers. 



LIFE-HISTORY STUDIES 



The evidence thus far has brought out the position, the nature, and 

 the relative importance of the different pathogene structures which are 

 present in or on the grain! Inoculation and incubation have been 

 touched upon, hul only in so far as was necessary for elucidation. For 

 sake of clarity, the writer believes thai each phase of the life history 

 of the two pathogenes— inoculation, incubation, and infection — should 

 now he presented separately. 



